0600-6-mt-1mark

If the temperature of atmosphere increases at constant absolute humidity, the percentage saturation would

• decrease

• remain constant

• increase

• none of these

0600-7-mt-1mark

If the temperature of atmosphere increases at constant absolute humidity, the wet-bulb temperature would

• decrease

• remain constant

• increase

• none of these

GATE-CH-1988-5-b-vi-mt-2mark

Air with a dry bulb temperature \(t_{d1}\) and a wet bulb temperature \(t_{w1}\) is passed through a heater and then through an adiabatic cooler from which it emerges with dry and wet bulb temperatures of \(t_{d2}\) and \(t_{w2}\) respectively. Then

• always \(t_{w1} > t_{w2} \mbox { and } t_{d1} > t_{d2}\)
  

• always \(t_{w1} < t_{w2} \mbox { and } t_{d1} > t_{d2}\)

• always \(t_{w1} > t_{w2} \mbox { and } t_{d1} < t_{d2}\)
  

• \(t_{w1} < t_{w2} \mbox { and } t_{d1} \mbox { can be greater than, equal to or less than } t_{d2}\)

GATE-CH-1990-5-v-mt-2mark

Lewis number = 1 signifies:

• \(\text {Pr} = \text {Sc}\)

• \(\text {Pr} = \text {Re}\)

• \(\text {Sc} = \text {Re}\)

• \(\text {Nu} = \text {Sh}\)

GATE-CH-1998-2-13-mt-2mark

For the Air-Water system under ambient conditions, the adiabatic saturation temperature and the wet-bulb temperature are nearly equal, because

• water has a high latent heat of evaporation

• Lewis number is close to unity

• they are always equal under all circumstances

• solubility of the components of air in water is very small

GATE-CH-1998-2-8-mt-2mark

Air, initially at 101.3 kPa and 40\(^\circ \)C, and with a relative humidity of 50%, is cooled at constant pressure to 30\(^\circ \)C. The cooled air has

• A higher dew point

• A higher absolute (specific) humidity

• A higher relative humidity

• A higher wet bulb temperature

GATE-CH-2001-1-13-mt-1mark

The Lewis relation for air-water humidification is given by (\(k_Y\): mass transfer coefficient of moisture in air; \(h_G\): heat transfer coefficient; \(C_S\): heat capacity of vapor-gas mixture)

• \(\displaystyle \frac {h_G^2}{k_YC_S} = 1\)

• \(\displaystyle \frac {k_YC_S^2}{h_G} = 1\)

• \(\displaystyle \frac {h_G}{k_YC_S} = 1\)

• \(\displaystyle \frac {k_Y^2h_G}{C_S} = 1\)

GATE-CH-2003-67-mt-2mark

The following plot gives the saturated humidity (\(H_e\)) versus Temperature (\(T\)).

Line joining \((H_1,T_1)\) and \((H_2,T_2)\) is the constant enthalpy line. Choose the correct one.

• \(T_1\) - Dew point Temp; \(T_2\) - Dry bulb Temp; \(T_3\) - Wet bulp Temp.

• \(T_1\) - Dew point Temp; \(T_2\) - Wet bulb Temp; \(T_3\) - Wet bulp Temp.

• \(T_1\) - Wet bulb Temp; \(T_2\) - Dry bulb Temp; \(T_3\) - Dew point Temp.

• \(T_1\) - Dry bulb Temp; \(T_2\) - Wet bulb Temp; \(T_3\) - Dew point Temp.

GATE-CH-2016-13-mt-1mark

For what value of Lewis number, the wet-bulb temperature and adiabatic saturation temperature are nearly equal?

• 0.33

• 0.5

• 1

• 2

GATE-MN-2013-41-mt-2mark

Four psychrometric processes \(P\), \(Q\), \(R\) and \(S\) are shown in the psychrometric chart below.

These processes respectively represent

• dehumidification, humidification, sensible heating, sensible cooling

• sensible heating, humidification, dehumidification, sensible cooling

• dehumidification, sensible heating, sensible cooling, humidification

• humidification, sensible heating, dehumidification, sensible cooling

GATE-CH-XE-2008-G-8-mt-1mark

If the moist air is heated at a constant pressure

• the specific humidity changes

• the relative humidity does not change

• the relative humidity decreases

• the relative humidity increases

GATE-CH-XE-2009-E-2-mt-1mark

During the adiabatic saturation process

• the relative humidity increases but the specific humidity remains constant

• both the relative humidity and the specific humidity remain constant

• both the relative humidity and the specific humidity increase

• the relative humidity decreases but the specific humidity increases

GATE-CH-1994-3-c-mt-1mark

If an insoluble gas is passed through a volatile liquid placed in a perfectly insulated container, the temperature of the liquid will increase. (True/False)

• True
• False

GATE-CH-1989-5-ii-e-f-mt-4mark

Air is passed through a heater at constant pressure. The inlet and outlet conditions of the air are as follows:
Inlet:
Dry bulb temperature = 31.7\(^\circ \)C
Wet bulb temperature = 23.9\(^\circ \)C
Humidity = 30%
Outlet:
Dry bulb temperature = 70\(^\circ \)C
(i) The inlet air will have a dew point
{#1}

(ii) In the above problem, the air from the heater will have a humidity:
{#2}

GATE-CH-2004-21-22-mt-2mark

An air-water vapor mixture has a dry bulb temperature of 60^oC and a dew point temperature of 40^oC. The total pressure is 101.3 kPa and the vapor pressures of water at 40^oC and 60^oC are 7.30 kPa and 19.91 kPa, respectively.

(i) The humidity of air sample expressed as kg of water vapor/kg of dry air is

{#1}

(ii) The wet bulb temperature \(T_w\) for the above mixture would be

{#2}

GATE-CH-1996-2-17-mt-2mark

In a mixture of benzene vapor and nitrogen gas at a total pressure of 900 mm Hg, if the absolute humidity of benzene is 0.2 kg benzene/ kg nitrogen, the partial pressure of benzene in mm Hg is

• 180

• 60.3

• 720

• 200

GATE-CH-1999-2-11-mt-2mark

If the specific heats of a gas and vapor are 0.2 kJ/kg.K and 1.5 kJ/kg.K respectively, and the humidity is 0.01, the humid heat in kJ/kg.K is

• 0.31

• 0.107

• 0.017

• 0.215

GATE-CH-2007-29-mt-2mark

If the percent humidity of air (30^oC, total pressure 100 kPa) is 24% and the saturation pressure of water vapor at that temperature is 4 kPa, the percent relative humidity and the absolute humidity of air are

• \(25.2, 0.0062\)

• \(25, 0.0035\)

• \(20.7, 0.0055\)

• \(18.2, 0.0035\)

GATE-CH-2010-38-mt-2mark

At 25^oC and 90% relative humidity, water evaporates from the surface of a lake at the rate of 1.0 kg/(m².h). The relative humidity that will lead to an evaporation rate of 3.0 kg/(m².h), with other conditions remaining the same, is

• 30%

• 50%

• 60%

• 70%

GATE-CH-ME-2008-53-mt-2mark

Moist air at a pressure of 100 kPa is compressed to 500 kPa and then cooled to 35^oC in an aftercooler. The air at the entry to the aftercooler is unsaturated and becomes just saturated at the exit of the aftercooler. The saturation pressure of water at 35^oC is 5.628 kPa. The partial pressure of water vapor (in kPa) in the moist air entering the compressor is closest to

• 0.57

• 1.13

• 2.26

• 4.52

GATE-CH-ME-2008-55-mt-2mark

Air (at atmospheric pressure) at a dry bulb temperature of 40^oC and wet bulb temperature of 20^oC is humidified in an air washer operating with continuous water recirculation. The wet bulb depression (i.e., the difference between the dry and wet bulb temperatures) at the exit is 25% of that at the inlet. The dry bulb temperature at the exit of the air washer is closest to

• 10^oC

• 20^oC

• 25^oC

• 30^oC

GATE-CH-ME-2010-42-mt-2mark

A moist air sample has dry bulb temperature of 30^oC and specific humidity of 11.5 g water vapor per kg dry air. Assume molecular weight of air as 28.93. If the saturation vapor pressure of water at 30^oC is 4.24 kPa and the total pressure is 90 kPa, then the relative humidity (in %) of air sample is

• 50.5

• 38.5

• 56.5

• 68.5

GATE-CH-ME-2012-A-31-mt-2mark

A room contains 35 kg of dry air and 0.5 kg of water vapor. The total pressure and temperature of air in the room are 100 kPa and 25^oC respectively. Given that the saturation pressure for water at 25^oC is 3.17 kPa, the relative humidity of the air in the room is

• 67%

• 55%

• 83%

• 71%

GATE-CH-XE-2010-E-16-mt-2mark

Air-water vapor mixture having 100% relative humidity at 50^oC is heated isobarically to 100^oC in a closed system. If saturation pressure at 50^oC is 12.352 kPa and at 100^oC is 101.42 kPa, final relative humidity is

• 0%

• 8.2%

• 12.2%

• 100%